Subminiature trimmer potentiometer



Dec. 16; 1969 H. B. CASEY ET AL 3,484,734

' SUBMINIATURE TRIMMER POTENTIOMETER Filed April 15, 1968 2 Sheets-Sheet 1 HA/P/PVE. CASEY JOH/V GWOODS GEORGE W. W000 Dec. 16, 1969 H. B. CASEY ET AL SUBMINIATURE TRIMMER POTENTIOMETER 2 Sheets-Sheet Filed April 15, 1968 United States Patent O ils. c1. 338-162 7 Claims ABSTRACT OF THE DISCLOSURE A subminiature trimmer potentiometer comprising a circular base having a non-circular post in the center thereof. A circular disk of an electrical insulating material having a non-circular opening in the center thereof is mounted on the base with the post extending through the opening in the disk. A resistance film is coated on the peripheral surface of the disk. A circular rotor is rotatably mounted over the disk. A metal contact is connected to the rotor to rotate therewith and slidably engages the resistance film. A cup-shaped cover is mounted on and secured to the base and encloses the disk and the rotor; The cover has an opening therethrough through which the rotor projects so that the rotor is accessible from outside the cover. Terminal wires are carried by the base with one of the terminal wires being electrically connected to the contact and the other terminal wires being electrically connected to the resistance film.

BACKGROUND With the trend in the electronics industry to making electronic equipment smaller and more compact, there has been developed an element for miniaturized and subminiaturized electrical components. In the electrical resistor field, a major problem in meeting thisdemand has been with regard to variable resistors, such as rheostats and potentiometers. In developing subminiature potentiometers, i.e. potentiometers as small as one-quarter inch in diameter, it has been found that merely reducing the size of previously used potentiometers is not satisfactory. If the parts of such previously used otentiometers are merely reduced in size, even by only one-half, the parts become so small that they are extremely difficult to make, handle and assemble together with the potentiometer. Therefore, it has been found necessary to redesign the potentiometers and minimize the number of parts making u the potentiometer sothat the parts can be easily made and then easilyand quickly assembled into the potentiometer.

SUMMARY OF INVENTION It is an object of the present invention to provide a novel construction of a subminiature trimmer potentiometer.

It is another object of the present invention to provide a subminiature trimmer potentiometer which is made up ofa minimum number of parts and which can be easily assembled.

It is a further object of the present invention to provide a subminiature trimmer potentiometer which can include a fixed resistance in a series-parallel arrangement with the variable resistance element of the potentiometer without increasing the size of the potentiometer.

Other objects will appear hereinafter.

BRIEF DESCRIPTION OF DRAWINGS For the purpose of illustrating the invention, there is shown'in the drawings forms which are presently pre- Patented Dec. 16, 1969 ferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIGURE 1 is a transverse sectional view of the trimmer potentiometer of the present invention.

FIGURE 2 is a bottom plan view of the trimmer potentiometer of the present invention.

FIGURE 3 is a sectional view taken along line 33 of FIGURE 1.

FIGURE 4 is a sectional view taken along line 4-4 of FIGURE 1.

FIGURE 5 is an exploded perspective view of the trimmer potentiometer of the present invention.

FIGURE 6 is a sectional view similar to FIGURE 4 but showing a modification of the trimmer potentiometer of the present invention which includes a fixed resistance in a series-parallel arrangement with the variable resistance element.

FIGURE 7 is a sectional view taken along line 7-7 of FIGURE 6.

DESCRIPTION OF INVENTION Referring to FIGURES 15 of the drawings, the trimmer potentiometer of the present invention is generally designated as 10. In general, potentiometer 10 comprises a cylindrical housing, generally designated as 12, which can be as small as one-quarter inch in diameter and approximately inch in height. A resistance element 14 is mounted in the housing 12, and a rotor 16 is rotatably mounted in the housing and projects through an opening in the housing. A contact 18 is carried by the rotor and slidably engages the resistance element 14. Three terminal wires 20, 22 and 24 extend through the housing with the terminal wires 20 and 22 being connected to the resistance element 14 and the terminal wire 24 being connected to the contact 18. Thus, rotation of the rotor 16 moves the contact 18 along the resistance element 14 to vary the resistance value setting of the potentiometer 10.

More specifically, the housing 12 comprises a base 26 and a cover 28. The base 26 is a flat, circular disk of an electrical insulating material, such as a plastic. The base has three notches 30 in its edges uniformally spaced therearound (see FIGURE 5). A non-circular post 32 is integral with and projects upwardly from the center of the base 26. A wedge-shaped stop lug 34 is integral with and projects upwardly from the base 26 adjacent the edge of the base.

As shown, the terminal wires 20, 22 and 24 are mounted on and secured to the base 26 during the molding of the base. The contact terminal wire 24 has an upper portion 24a which extends upwardly through the center of the post 32 and projects above the top of the post (see FIGURE 1). The resistor terminalwires 20 and 22 have upper portions 20a and 22a respectively which extend upwardly from the top surface of the base 26 at opposite sides of the stop lug 34 (see FIGURE 4). The terminal wires 20, 22 and 24 have intermediate bent portions 20B, 22b and 24b respectively which are completely within and extend across a portion of the base 26 so as to mechanically secure the terminal wires to the base.

The cover 28, which is made of metal,- is cup-shaped having a cylindrical outer wall 36 and a flat, circular top Wall 38. The outer wall 36 of the cover 28 is mounted on the base 26. Three spaced tabs 40 project from the end of the outer wall 36 (see FIGURE 5). The tabs 40 extend through the notches 30 in the base 26, and as shown in FIGURE 2, are bent across the bottom surface of the base to secure the cover 28 to the base. The top wall 38 of the cover 28 has a circular, central opening 42 therethrough.

Resistance element 14 comprises a flat, circular disk 44 of an electrical insulating material, such as a ceramic or plastic having a non-circular opening 46 through the center thereof which is of the same size and shape as the post 32 on the base 26. The disk 44 is seated on the base 26 with the post 32 extending through the opening 46 of the disk so as to prevent relative rotation between the disk and the base. The disk 44 is of a thickness substantially the height of the post 32 and of a diameter to extend to the stop lug 34. A film 48 of a resistance material is coated on and extends almost completely around the peripheral edge of the disk 44. The resistance film 48 may be of any well-known electrical resistance materia such as carbon or a metal either with or without a binder The resistance film 48 has spaced apart ends which are positioned adjacent opposite sides of the stop lug 34. Termination films 50a and 50b of an electrically conductive metal are coated across the edge of the disk 44 at the ends of and contacting the resistance film 48. As shown in FIGURE 4, the upright portions and 22a of the resistor terminal wires 20 and 22 extend along the termination films 50a and 50b and are electrically connected thereto by either a solder or an electrically conductive cement. Thus, the resistor terminal wires 20 and 22 are electrically connected to opposite ends of the resistance film 48. This also mechanically secures the resistance element 14 to the base 26 of the housing 12. A thin, circular sheet 52 of an electrical insulation material, such as a plastic, is seated on the top of the resistance element 14 and extends radially slightly beyond the edge of the resistance element.

Rotor 16 comprises a circular disk 54 of an electrical insulation material, such as a plastic, of a diameter greater than the diameter of the resistance element 14 but less than the internal diameter of the cover wall 36 and of a thickness substantially equal to the distance between the resistance element 14 and the top wall 38 of the cover 28. A circular hub 56 is integral with the projects upwardly from the center of the disk 54. The hub 56 is of a diameter substantially equal to the diameter of the opening 42 in the top wall 38 of the cover 28 and projects through the opening 42 so as to be accessible from outside the cover. A transverse slot 58 is provided across the top surface of the hub 56. The slot 58 is adapted to receive a screw driver or similar tool to rotate the rotor 16. A wedge-shaped stop lug 60 projects radially from the edge of the disk 54. The sides of the stop lug 60 are tapered to mate with the tapered sides of the stop lug 34 on the base so that engagement of the rotor stop lug 60 with the base stop lug 34 limits the degree of rotation of the rotor 16. A pair of spaced, parallel notches 62 are provided in the outer edge of the stop lug 60. A blind hole 64 is provided in the center of the bottom surface of the disk 54. The hole 64 is of a diameter substantially equal to the diameter of the contact terminal wire 24 so that the upright portion 24a of the contact terminal wire 24 fits into the hole 64. An annular groove 76 is provided in the upper surface of the rotor disk 54 at the edge thereof. An annular sealing ring 78 is seated in the groove 76 and engages both the rotor disk 54 and the inner surface of the top wall 38 of the cover 28 so as to seal the passage between the cover and the rotor.

Contact 18 comprises a thin, fiat circular plate 66 of an electrically conductive metal. An arm 68 is integral with and projects radially from the plate 66. The arm 68 extends under the stop lug 60. A pair of drive lugs 69 extend upwardly from opposite sides of the arm 68 and fit into the notches 62 in the rotor stop lug 60. A flange 70 is integral with and extends down wardly from the end of the arm 68. A pair of parallel spring fingers 72 are integral with and extend from a side edge of the flange 70. The fingers 72 extend back along the flange between the fiange and the resistance element 14 and the ends of the fingers slidably engage the resistance film 48 of the resistance element. A hole 73 is provided in the center of the plate 66 and a tab 74 is lanced out of the center of the plate 66 at the edge of the hole 73. As shown in FIGURE 1, the end of the upright portion 24a of the cotnact terminal wire 24 extends through the hole 73 in the contact plate 66. The hole 73 is smaller than the contact termination wire 24 so that the tab 74 is bent slightly upwardly. Thus, the tab resiliently engages the contact terminal wire 24. Thus, the contact 18 is connected to the rotor 16 so as to rotate therewith, and is electrical connected to both the resistance film 48 and the contact terminal wire 24 so as to electrically connect the resistance element 14 to the contact terminal wire 24.

To assemble the potentiometer 10 of the present invention, the resistance element 14 is first placed on the base 26 and the resistor terminal wires 20 and 22 connected to the termination films 50a and 50b. After the insulating sheet 52 is placed over the resistance element 14, the contact 18 is mounted on the contact terminal wire 24 with the drive lugs 69 extending upwardly. The rotor 16 is then placed over the contact 18 with the drive lugs 69 fitting into the notches 62. With the sealing ring seated on the rotor 16, the cover 28 is mounted on the base 26 with the rotor hub 56 extending through the opening 42 and the cover tabs 40 extending through the notches 30 in the base. The cover tabs 40 are then bent under the base 26 to secure the cover 28 to the base and complete the assembling of the potentiometer. Thus, it can be seen that the potentiometer 10 is made up of a minimum number of parts which can be easily and quickly assembled even though the parts may be very small in size.

Referring to FIGURES 6 and 7, there is shown a modification of the potentiometer of the present invention, generally designated as 10 which includes a fixed resistance electrically connected in a series-parallel arrangement with the variable resistance element. Potentiometer 10 is identical in construction to the potentiometer 10 described above except as to the construction of the resistance element 14 and the contact terminal wire 24 The resistance element 14 comprises a fiat, circular disk 44 of an electrical insulating material having the non-circular opening 46 in the center thereof which receives the non-circular post 32 of the base 26 A variable resistance film 48 and a fixed resistance film are coated on the peripheral edge of the disk 44 with the length of the variable resistance film 48 around the edge of the disk 44 being much greater than the length of the fixed resistance film 80. The variable resistance film 48 extends from adjacent one side of the base stop lug 34 to a point slightly spaced from the other side of the base stop lug. The fixed resistance film 80 extends across the end of the base stop lug 34 A termination film 50b extends across the edge of the disk 44 at the end of the variable resistance film 48 which is adjacent the stop lug 34 The termination film 5011 is also electrically connected to one end of the fixed resistance film 80. The upright portion 22a of the resistor terminal wire 22 is connected to the termination film 50b by either solder or an electrically conductive cement. A termination film 82 is coated across the edge of the disk 44 at the other end of and contacting the fixed resistance film 80. The upright portion 20a of the resistor terminal wire 20 is connected by either solder or an electrically conductive cement to a termination film 50a coated across the edge of the disk 44 at the other end of the variable resistance film 48 The contact terminal wire 24 is U-shaped having a base 84 and a pair of parallel legs 86 and 88. The base 84 of the contact terminal wire 24 is embedded in and extends radially along the base 26 of the housing. The leg 86 extends upwardly along the center of the post 32 of the housing base 26 and projects beyond the top of the post 32 The end of the leg 86 extends through the hole 73 in the contact 18 and is contacted by the tab 74 of the contact 18 The leg 88 extends upwardly from the housing base 26 along the fixed resistor termination film 82, and is connected thereto by either solder or an electrically conductive solder. Thus, the fixed resistance film 80 is electrically connected between the resistor terminal wire 22 and the contact terminal wire 24 and is electrically connected in a series-parallel arrangement with the variable resistor film 48 through the contact terminal wire 24 and the contact 18 As the contact fingers 72 are moved along the variable resistance film 48 by rotating the rotor 1-6 the resistance value of the potentiometer between the resistor terminal wires 20 and 22 is the resistance value of the portion of the variable resistance film 48 between the resistor terminal wire 20 and the contact fingers 72 plus the parallel arrangement of the resistance values of the fixed resistance film 80 and the remaining portion of the variable resistance film.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

We claim:

1. A trimmer potentiometer comprising:

a cylindrical housing having a circular base and a cupshaped cover mounted on and secured to said base, said base having a non-circular post projecting from the center of the inner surface thereof, and the cover having a circular opening in its surface opposite the base;

a resistance element seated on the inner surface of said base, said resistance element comprising a circular disk of an electrical insulating material having a central non-circular opening therethrough through which the post on the base extends, and a film of an electrical resistance material coated on the peripheral edge of the disk;

a rotor rotatably mounted in the housing over the resistance element, said rotor having a hub projecting through the opening in the cover so as to be accessible from outside the housing;

a metal contact mounted within the housing and drivingly connected to said rotor, said contact having a finger slidably engaging the resistance film, a pair of resistance terminal wires extending through and secured to the base of the housing, said resistance terminal wires being electrically connected to said resistance film at spaced points along the resistance film; and a contact terminal wire carried by said base, said contact terminal wire having an end portion extending along the center of the post of the base and slidably engaging the contact.

2. A trimmer potentiometer in accordance with claim 1 in which the contact comprises a flat, metal plate mounted between the rotor and the resistance element, an arm extends from the plate beyond the edge of the resistance element, a flange extends from the arm across the peripheral edge of the resistance element and the finger extends from the flange between the flange and the resistance element and slidably engages the resistance film.

3. A trimmer potentiometer in accordance with claim 2 in which the contact plate has a hole therethrough and a tab extending from the plate at the edge of the hole, and the end portion of the contact terminal wire extends through said hole in the contact plate and slidably engages said tab on the contact plate.

4. A trimmer potentiometer in accordance with claim ,2 in which the rotor has a pair of spaced, parallel notches therein and the contact has a pair of drive flanges projecting therefrom and extending into the notches in the rotor so as to drivingly connect the contact to the rotor.

5. A trimmer potentiometer in accordance with claim 1 in which a stop lug projects from the inner surface of the base across the peripheral edge of the resistance element, the rotor has a stop lug projecting from the edge thereof which is adapted to engage the sides of the base stop lug to limit the degree of rotation of the rotor, the resistance film extends around the edge of the resistance element disk from one side of the bases top lug to the other side of the base stop lug, and the resistance terminal wires are connected to the resistance film at the sides of the base stop lug.

6. A trimmer potentiometer in accordance with claim .1 including a second resistance film coated on the peripheral edge of the resistance element disk, one end of said resistance film being electrically connected to one end of the first said resistance film, and the contact terminal wire has a second end portion which is electrically connected to the other end of the second resistance film.

7. A trimmer potentiometer in accordance with claim 6 in which the contact terminal wire is U-shaped having a base and a pair of spaced parallel legs, the base of the contact terminal wire being embedded in the base of the housing with one leg of the contact terminal wire extending along the center of the post on the base and engaging the contact, and the other leg of the contact terminal wire projecting from the inner surface of the base along the peripheral edge of the resistance element and being electrically connected to the other end of the second resistance film.

References Cited UNITED STATES PATENTS 3,377,605 4/ 1968 Baskett 338-162 3,193,286 7/1965 Moore et al. 338-164 3,111,640 11/1963 Dial 338-184 X 3,377,606 4/1968 Ferrell 338-202 X 2,812,408 11/1957 Williford 338-202 X 2,259,792 11/ 1941 Batcheller 338-202 X 2,098,273 11/1937 Bradley et a1 338-202 X LEWIS H. MYERS, Primary Examiner A. T. GRIMLEY, Assistant Examiner US. Cl. X.R. 338-164, 171, 184 

